EP 949 390 discloses two generally co-planar panels supported almost edge-to-edge by an intermediate beam. A coupling member is captive to the beam by inter-engaging longitudinal formations and provides an interlocking engagement for the edges of the panels. Opposite the coupling member the beam is proud of the panels and receives and retains a cap which seals against the panels. Downwardly directed wings in the cap engage upwardly directed channels in a base thereof and prevent side walls of the cap from splaying apart.
WO 2008/149344 in the name of the present Applicant discloses an assembly for securing to a structure two juxtaposed panels, each including a first surface, an opposing second surface and a joining flange located at, or adjacent to, respective juxtaposed edges thereof. The assembly is particularly configured to prevent splaying apart of the juxtaposed panels under load and employs a retaining member that is fixedly mounted to the support structure and to which there is attached a clamping member having two spaced-apart legs depending from a web, each leg being configured to engage a respective exposed surface of an adjacent joining flange. A fastening means is provided for fastening the retaining member to a construction element that inhibits angular displacement of the panels when force is applied to either the first or second surfaces thereof.
U.S. Pat. No. 6,164,024 discloses a light transmissive glazing panel system for overhead roof constructions where glazing panels are supported on a framework and include upstanding seam flanges for connecting adjacent panels together with a joining connector. FIGS. 4 and 13 show arrangements where panels having upwardly projecting flanges on their mating edges are juxtaposed on opposite sides of aluminum support brackets that are bolted to the roof structure and a clamping member is then disposed on the projecting flanges to secure and seal the structure.
The above publications are typical of prior art that discloses the mounting of extruded panels to a construction element. The linear coefficient of thermal expansion (α) of polycarbonate at 23° C. is 65-70×10−6/° C., which is approximately three times that of aluminum for which α at 20° C. is 23×10−6/° C. To the extent that some kind of retaining member is fixedly mounted to the construction element, it is to be understood that this is incapable of movement. But the polycarbonate panels mounted thereto do expand and contract, thus becoming subject to tensile and compressive forces. Specifically, adjacent panels that expand will push against each other laterally, thus subjecting their respective mounts to compressive forces. This gives rise to high frictional forces between the panels and the mounts, which militates against thermal expansion of the panels in the longitudinal direction, which can cause buckling or other distortion of the panels.
Normally the clamping members are formed of the same or similar material to the panels, e.g. polycarbonate, such that the clamping members tend to expand at the same rate as the panels. Therefore in structures such as shown in FIGS. 7, 8 and 11 of WO 2008/149344 where the clamping members are fixedly mounted to the support structure, and are thus restrained from expanding, the panels being tightly clamped by the clamping member are likewise unable to expand.
U.S. Pat. No. 6,536,175 discloses a panel assembly and joining elements having reciprocally engaged inclined surfaces facing inwards. FIG. 7 of this patent discloses a polycarbonate jointing element fastened to a metal plate in the form of a track for connection to load bearing structures. However, the arrangement is not directed to the need to allow for longitudinal thermal expansion. Moreover, in order to ensure a waterproof seal there is provided a pressing element having a conical shape at the tip, which is inserted between two downwardly projecting joining flanges of adjacent panels so as to urge the flanges apart and thus press them tightly against opposing internal walls of the polycarbonate jointing element. It is apparent from FIG. 7 of the patent that this also urges the walls of the jointing element against the metal track thereby increasing friction between the track and the jointing element and militating against sliding of the jointing element within the metal track.
EP 1 111 153 discloses a glazing system comprising a plurality of plastic glazing panels each having at least one edge region juxtaposed with the edge region of the other panel. The juxtaposed edges have an abutment extending transversely of the plane of each glazing panel. A support structure at least partially encloses the abutments to deter separation of the glazing panels from the support structure.
US 2010/132293 discloses an internal structural mullion for a standing seam panel system. A two-piece assembly includes a main extrusion having one hooked portion and a secondary extrusion having an opposing hooked portion. A cavity is defined on the main extrusion, and the secondary extrusion includes a foot which upon insertion into the cavity forms a fulcrum about which the secondary extrusion can bend away from the main extrusion and be tightened or loosened by the tightening or loosing of a screw, as a result forming a clamp for engaging panels of the panel system with variable pressure.
US 2003/188500 discloses a panel clip assembly for use with skylight or roof panel systems and having allowance for reduced movement of panels both parallel and perpendicular to the seam formed by adjoining panels.
US 2005/102943 discloses a clip assembly for securing standing seam skylight or roofing panels to substrates and including a first clip member and a second clip member each having an upright member and an upper flange member and a lower flange member extending therefrom. A gap is formed between the upright member of the first clip member and the upright member of the second clip member and a base allows the assembly to slide.
DE 203 09 516 discloses a retainer comprising at least two polycarbonate plates forming chambers and a number of cross pieces with corresponding secure fixings.